1. Field of the Invention
This invention concerns a process and apparatus for examining the dimensions of shoe-lasts, for determining the directions defining or determining the measurements and the manufacturing process by forming projection drawings.
2. Description of the Prior Art
Current large-scale footwear manufacture employs numerous tools which follow the shape of a last. Prefabricated components are widely used, which are frequently obtained from other firms or enterprises. The use of injection moulding technology and of prefabricated sole shapes has become particularly widespread. An international agreement has been reached for conversion to the metric system. With this, an agreement on dimensions or sizes between various enterprises has become inevitable, as have uniform or single interpretation of dimensions and standardisation.
The fundamental determinant of dimensions is the last and the different components such as insole, sole, heel, upper etc., are based on this.
It is a fundamental requirement that the dimensions of these various components should be coordinated or harmonised with a relatively high accuracy. The different sizes cause a special problem because they grow or reduce in a geometrical, rather than arithmetical, progression relative to a predetermined mean value.
The shape of a last generally follows the shape of a foot and its dimensions could only be characterised mathematically by an infinite number of data. In current practice, however, even the determination of a few extremely important main dimensions, and their monitoring, causes a severe problem to experts. In practice, the number of measurements performed result in as many different sizes because the direction of the measurement cannot by simple means be indicated unambiguously and reproducibly. The published patents in this field have as a chief common characteristic that they emphasise size drawings; these known patents include some by the inventors of the present invention. In other words, these devices provide information about the distribution of measurements or sizes within a given last, but the comparison of different lasts and types performed with them results in a large error percentage. The significance of the direction of measurement has already been recognised both by the present inventors and by others. In the interest of reproducibility of the direction of measurement, special direction-determining devices have been constructed. The chief characteristic of these devices can be summarised in that the known and tabulated spatial relationships of a few characteristic points of a last are adjusted or set by intricate devices and the last is then fitted to these measurement points. Such devices have only come into moderate use because their handling and use is complicated, their manufacture is expensive, and also because the coordination of just a few points still only gives very little information about the spatial configuration of a complicated last shape. However, to increase the number of measurement points makes it impossible to fit the last and to allow it to be observed.
One must also reckon with the fact that a separate direction indicating device also has its own separate inherent measurement error.
For the above reasons, the inventors have already attempted to construct a mechanism which, in addition to the control and registration or recordal of a large number of dimensions, also attempted to indicate the measurement direction for different lasts in one apparatus. But these mechanisms also have had the defect that they operated by using measurement points and that they presuppose the existence of an accurate insole master or template which had to be laid on the sole surface of the last. Unfortunately, practice has shown that one could not obtain sufficient accuracy with this apparatus and a further problem is caused by the fact that the curvature or tip bend of the last may vary. Furthermore, one could not decide the appropriateness of the different sizes of the series and one could not determine the errors in displaying a series.
We have already recognised earlier that not only the control but also the manufacture should be performed with a constant predetermined spatially-directed last gripping if we wish to manufacture end sizes of the same dimensions even where the display of the series took place from completely identical master lasts. The designing and dimensioning of the last series cannot therefore be exhausted by comparing the identity of or the differences between two types of models.
The individual dimensions of the components can only be completely harmonised and coordinated if the direction of the manufacture and dimensional control of the last series are identically selected.